Gradle Java FX aplication Build failed: UnsupportedClassVersionError

Question

I am making JavaFX application as a university assignment and I want to include a .exe file of the application. However, while trying to build the application gradlew run I ran into java.lang.UnsupportedClassVersionError. My build.gradle:

plugins {
    id 'java'
    id 'application'
    id 'org.openjfx.javafxplugin' version '0.0.8'
}


version '1.0-SNAPSHOT'


repositories {
    mavenCentral()
}

dependencies {
    testCompile group: 'junit', name: 'junit', version: '4.12'
}

javafx {
    modules = [ 'javafx.controls', 'javafx.fxml' ]
    version = '13'
}

run{
    standardInput = System.in
    standardOutput = System.out
}

jar {
    from {
        configurations.runtime.collect {
            it.isDirectory() ? it : zipTree(it)
        }
        configurations.compile.collect {
            it.isDirectory() ? it : zipTree(it)
        }
    }
    manifest {
        attributes 'Main-Class': 'java.frontend.Main'
    }

    exclude 'META-INF/*.RSA', 'META-INF/*.SF','META-INF/*.DSA'
}

mainClassName = 'frontend.Main'

project structure

If I try to use grade -> build -> build and run the build/libs/"the built file" I have two errors:

Error: Could not find or load main class java.frontend.Main
Caused by: java.lang.ClassNotFoundException: java.frontend.Main